This invention relates to an improved method of making an improved mold by forming a rigid ceramic casing around a plurality of mold sections to hold them against movement relative to each other during a casting operation. The mold is advantageously utilized to form a plurality of relatively small articles.
A method and apparatus for casting a plurality of relatively small articles is disclosed in U.S. Pat. No. 3,786,857. This patent discloses a mold formed by a plurality of discs arranged in a stack. Each of the mold discs cooperates with an adjacent disc to define at least one mold cavity. The stack of mold discs is immersed in a body of molten metal. Molten metal flows inwardly through openings in the outside of the stack to the mold cavities within the stack. Since the stack of mold discs is unenclosed, difficulty could be encountered with molten metal flowing between the various mold discs if the molten metal was forced into the mold cavities under pressure.
It has been proposed to enclose a plurality of mold discs with a metal casing to support the mold discs in the manner disclosed in U.S. Pat. No. 1,358,435. Although the metal casing does, to some extent at least, support the mold discs, it blocks the escape of gas from the mold cavities. To accommodate the escape of gas from the mold, paper sheets are placed between each of the mold discs and are burned as molten metal is poured into the mold. Of course, burning the paper sheets between the discs provides a space between the mold discs which may fill with molten metal to provide objectionable flash or run-out during a casting operation.
In addition to the aforementioned patents, U.S. Pat. Nos. 3,628,598 and 3,656,539 disclose the use of a stack of mold sections to form a plurality of parts. These patents contemplate that the molten metal will be forced into the mold cavities by the use of a fluid pressure differential.